diff --git a/Lib/test/test_codeccallbacks.py b/Lib/test/test_codeccallbacks.py
index c5b1e25..e656d2f 100644
--- a/Lib/test/test_codeccallbacks.py
+++ b/Lib/test/test_codeccallbacks.py
@@ -744,7 +744,7 @@
                 raise ValueError
         self.assertRaises(UnicodeError, codecs.charmap_decode, b"\xff", "strict", {0xff: None})
         self.assertRaises(ValueError, codecs.charmap_decode, b"\xff", "strict", D())
-        self.assertRaises(TypeError, codecs.charmap_decode, b"\xff", "strict", {0xff: sys.maxunicode+1})
+        self.assertRaises(TypeError, codecs.charmap_decode, b"\xff", "strict", {0xff: 0x110000})
 
     def test_encodehelper(self):
         # enhance coverage of:
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 3426a4d..f342d88 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -1546,6 +1546,10 @@
             ("abc", 3)
         )
 
+        self.assertRaises(UnicodeDecodeError,
+            codecs.charmap_decode, b"\x00\x01\x02", "strict", "ab"
+        )
+
         self.assertEqual(
             codecs.charmap_decode(b"\x00\x01\x02", "replace", "ab"),
             ("ab\ufffd", 3)
@@ -1572,6 +1576,107 @@
             ("", len(allbytes))
         )
 
+    def test_decode_with_int2str_map(self):
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: 'a', 1: 'b', 2: 'c'}),
+            ("abc", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: 'Aa', 1: 'Bb', 2: 'Cc'}),
+            ("AaBbCc", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: '\U0010FFFF', 1: 'b', 2: 'c'}),
+            ("\U0010FFFFbc", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: 'a', 1: 'b', 2: ''}),
+            ("ab", 3)
+        )
+
+        self.assertRaises(UnicodeDecodeError,
+            codecs.charmap_decode, b"\x00\x01\x02", "strict",
+                                   {0: 'a', 1: 'b'}
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "replace",
+                                  {0: 'a', 1: 'b'}),
+            ("ab\ufffd", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "replace",
+                                  {0: 'a', 1: 'b', 2: None}),
+            ("ab\ufffd", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "ignore",
+                                  {0: 'a', 1: 'b'}),
+            ("ab", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "ignore",
+                                  {0: 'a', 1: 'b', 2: None}),
+            ("ab", 3)
+        )
+
+        allbytes = bytes(range(256))
+        self.assertEqual(
+            codecs.charmap_decode(allbytes, "ignore", {}),
+            ("", len(allbytes))
+        )
+
+    def test_decode_with_int2int_map(self):
+        a = ord('a')
+        b = ord('b')
+        c = ord('c')
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: a, 1: b, 2: c}),
+            ("abc", 3)
+        )
+
+        # Issue #15379
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "strict",
+                                  {0: 0x10FFFF, 1: b, 2: c}),
+            ("\U0010FFFFbc", 3)
+        )
+
+        self.assertRaises(TypeError,
+            codecs.charmap_decode, b"\x00\x01\x02", "strict",
+                                   {0: 0x110000, 1: b, 2: c}
+        )
+
+        self.assertRaises(UnicodeDecodeError,
+            codecs.charmap_decode, b"\x00\x01\x02", "strict",
+                                   {0: a, 1: b},
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "replace",
+                                  {0: a, 1: b}),
+            ("ab\ufffd", 3)
+        )
+
+        self.assertEqual(
+            codecs.charmap_decode(b"\x00\x01\x02", "ignore",
+                                  {0: a, 1: b}),
+            ("ab", 3)
+        )
+
+
 class WithStmtTest(unittest.TestCase):
     def test_encodedfile(self):
         f = io.BytesIO(b"\xc3\xbc")